Dry Suit Diving Larry “Harris” Taylor, Ph.D. Diving Safety Coordinator, U of Michigan © Larry P. Taylor, Ph.D. All Rights Reserved LPT Your Instructor U of MI Diving Safety Coordinator AAUS sanctioned Diving Safety Officer Internationally rated 3 - star instructor (CMAS) National Master Scuba Instructor (President’s Council) > 100 Diving Certifications > 100 Diving Publications > 1,200,000 visitors to “Diving Myths & Realities” web site Library: one of the best resources in North America Scuba Diver since 1977 Scuba Instructor since 1980 DAN Instructor since 1991 EANx Instructor since 1992 Ph.D. Biochemistry LPT Lecture is a Democracy! You control speed with your questions LPT The Water-work is Dictatorship! Do as instructed or leave the water LPT Knowledgeable, Physically Fit Divers GospelAccording to “Harris” Have More Fun! LPT Three Great Truths: Diving Is Fun Being Cold Is NOT Fun Wet & cold divers subsidize those diving warm & dry Wet-suited divers: Cold, On deck Dry-suited divers: Enjoying third dive LPT Must Understand Heat Loss to Protect From the Cold MIDDLE COAST LPT Ignoring (or Not Understanding) Heat Loss It is always the “not known” that poses the greatest risk LPT Heat LPT Heat is a Fluid Flows from hotter to colder until temperatures are equal Cannot stop movement Protection comes from slowing process LPT Thermal Balance Heat Out: Environment Conduction Convection Radiation Heat In: Cooling Metabolism Respiration Muscle Movement Perspiration Environment Excretion Conduction Disease Radiation LPT In-Water Heat Loss LPT Thermal Loss: Conduction Water removes heat ~ 25 x faster than dry, still air at same temperature Direct transfer of energy at the molecular level Major source of in-water heat loss Heat loss to water Heat loss warming breathing gas LPT Thermal Loss: Convection Moving liquid removes heat Continual process Wet suits restrict convective flow LPT Thermal Loss: Radiation Emission of infra red radiation Minor problem in the water LPT Thermal Loss: Evaporation / Respiration Change of state: Liquid gas Requires energy 9.72 kcal / mole Pre-dive sweating Insensible perspiration Humidifying dry breathing gas LPT Humans are Tropical Critters Better coping with heat than cold LPT Simplistic View of a Biochemist: Heat = Life Cold Robs Heat No Heat = No Life Heat LPT Body Response to Temperature Loss First Shiver: Abort the dive! LPT Estimated Unprotected In-Water Survival Time LPT Wind Chill Can Lead to Substantial Heat Loss LPT Cold Cold: Major physiological stressor Major obstacle to diving participation Major obstacle to limited bottom time This is a course in NOT being cold LPT Not Being Cold LPT Commercial Divers Often Use Hot Water Suits Surface supplied: Tether Breathing mix Communications Hot water LPT Historic Thermal Protection Schemes LPT The Layer Concept LPT Three Layers of Thermal Protection Layers varied depending on Environmental conditions Workload Personal Comfort LPT First Layer: Next to Skin Purpose: Keep Skin Dry Hydrophobic microfiber wicks water away from skin Dry skin loses heat much slower than moist skin LPT First Layer: Next to Skin Polypropylene Capilene Dry Base Dry Max (Socks) Must be synthetic material (all natural fibers absorb water) Different weights available (dependent on temperatures/workload) LPT Hydrophobic Materials Soon Acquire a Foul Body Smell (Body oils stick to hydrophobic material and turn rancid) Wash with breathable fabric detergent, (tiny amount of detergent) in cold water then smell the garment Detergent Molecule This end dissolves in water This end sticks to grease/hydrophobic material If detergent odor present: (This “stuck” detergent can absorb water / lessen insulation) Wash with only cold water until detergent smell is gone On trips, best to have multiple sets of first layer garment LPT Second Layer: Insulation Primary resistance to heat loss Fabric is matrix to hold trapped gas (the insulator) Insulation value = DT A t heat loss DT : temperature difference A : cross-sectional area t: time Heat loss depends on: Temperature difference across barrier Thickness & area of insulation Thermal resistance of insulator Time LPT Second Layer: Insulation Cotton (cellulose) is a No! No! Cotton is a poly-sugar Every –OH can grab water All natural fibers absorb water Water decreases insulation LPT Cellulose (Cotton) Ability to hold water makes cotton a “great’ summer fabric perspiration “grabbed” by cotton fibers water evaporates evaporation takes heat result is a cooling effect Ability to hold water makes cotton an undesirable in-water fabric evaporative cooling promotes heat loss & hypothermia water removes heat ~ 25 x faster than dry still air of same temperature Fogery : > 50% wilderness deaths a result of wearing cotton jeans Yosemite Rangers: wearing cotton in winter “death-seeking behavior” LPT Second Layer: Insulation Shape of insulator affects heat loss Best Resistance : planar surface (at right angles to heat flow) In general: Planar > cylindrical > spherical LPT Second Layer: “Wooly Bears” Wool or synthetic “pile” Very comfortable next to skin Warm, as long as dry Loses insulation rapidly when wet Loses insulation when compressed Decent insulation at reasonable price Least expensive protection Pile may clog valves Value based on # fibers / area; not weight LPT Second Layer: Open Cell Foam Synthetic foam open cell structure First compression resistant underwear Warm when dry Holds insulation at depth Rapidly loses insulation when wet Foam structure a bit non-flexible LPT Second Layer: Type b Marine Thinsulate Synthetic microfilament polypropylene Compression resistant Warm when dry Holds insulation at depth Holds insulation (~85 %) when wet Expensive Best insulation for wet environments LPT Second Layer: Type b Marine Thinsulate Smaller cell size traps more air (insulator) Requires more convective / conduction steps to transverse garment LPT Second Layer: Polartec Polatec: series of > 300 synthetic hydrophobic fabrics Polyester: polyethylene terephthalate (PET) Napped (fuzzy) insulator Can serve as Layer 1 Layer 1 & 2 combined Layer 1, 2 , & 3 (with waterproof shell) Depends on weight and design of fabric LPT Second Layer: Radiant Barrier Metallic heat reflective coat underneath cloth layer Radiant barriers work extremely well in a vacuum Reasonable in sealed, dry, surface garments Not effective underwater Experimental in the 1980’s Sold under brand name Underwave Did not stay long on the market Occasionally surfaces on e-bay LPT Second Layer: Blue Heat Active electrical heating system Boots, gloves, and full torso sold separately Lasts about 2 hours on 100% power Designed to supplement, not replace, thermal undergarments Very expensive Concern that heating may increase DCI risk Use on lowest power Best used on final ascent LPT Second Layer: Insulating Gas Primary insulation: thermal resistance of gas in the suit Thermal conductivity: the quantity of heat transmitted through a unit thickness of a material - in a direction normal to a surface of unit area - due to a unit temperature gradient under steady state conditions (measured in watts per meter Kelvin, W/(m . K). Examples: The lower the value, Air, atmosphere (gas) 0.024 The better the insulation Argon (gas) 0.016 Carbon dioxide (gas) 0.0146 Helium (gas) 0.142 Nitrogen (gas) 0.024 Water (liquid) 0.58 LPT Second Layer: Insulating Gas Carbon Dioxide (CO2) Tried because of thermal conductivity Readily available and inexpensive CO2 + H2O H2CO3 (carbonic acid) Carbonic acid creates itching and rashes Argon (Ar) Studies show little value (as practiced) when used with air diving (Effective with 6 fill/empty cycles to provide all Argon insulation) Valuable when diving tri-mix (N2, He, O2; heli-air) or heliox (Can’t use breathing gas ‘cause of heat loss with helium) LPT Second Layer: Argon Inflation System Valve on Bottom Easier to control Connects to Suit Inflator May need 2 cylinders: One to fill/flush 6 times One for dive LPT Second Layer: Aerogel ? Low density, open-cell nanopore structure ~ 20 nm cells approximate air molecule movement in vacuum Structure is ~ 95% air Extremely low thermal conductivity Expensive: US Navy experimental dive suit; $ 5,200,000 Underwear was 1,200,000 LPT Insulation Value Comparisons Thinsulate holds thermal protection even when submerged LPT Insulation Dry Value Comparisons Top four are aerogels LPT LPT From 1982: Personal Test of Diving Underwear LPT From 1982: Personal Test of Diving Underwear LPT The bottom line in underwear selection No single underwear package will Work in all combinations of water temperature and workload Divers need multiple packages Experience needed to match package with diving conditions Multiple divers on the same site may have different packages But, each will have individually correct system for their needs LPT LPT LPT LPT LPT LPT LPT LPT LPT LPT LPT LPT Third Layer: Gore Tex Short for Gore’s textile fabric Used for outdoor wear; not intended for in-water use Gore Tex membrane: Excludes water droplets Passes water vapor 9 billion pores per square inch Each pore 20,000 x smaller than water droplet Wash with warm water & breathable fabric detergent; no fabric softener or bleach LPT Third Layer: Dry Suits Keeps the insulation dry Protects insulation from abrasion Allows efficient, reliable cold water diving LPT Wet vs. Dry Suits LPT Summary of Wet Suit Properties Insulation: gas trapped in neoprene material tight fit restricts water flow (conductive / convective heat loss) Advantages: inexpensive reasonable protection in temperate water environments